Thermal imaging tube having a pyroelectric target and annular potential stabilizing electrode

ABSTRACT

A pyroelectric vidicon having an annular metal electrode on the beam side of the target for maintaining the perimeter of the target at a fixed potential.

United States Patent Crowell Dec. 23, 1975 THERMAL IMAGING TUBE HAVING A[56] References Cited PYROELECTRIC TARGET AND ANNULAR UNITED STATESPATENTS POTENTIAL STABILIZING ELECTRODE 2,900,569 8/1959 Cope 313/39Inventor: Merton H- Crowe Mahopac at al. 3,054,917 9/1962 Eberhardt313/388 [73] Assigneez North American Philips 3,259,791 7/1966 Jensen etal.... 313/387 Corporation, New York, NY. 3,278,783 10/1966 Brissot eta1. 250/338 [22] Filed Sept 9 1974 3,774,043 11/1973 Le Carvennec250/333 [21] Appl, NO; 504,373 Primary Examinerl-larold A. DixonAttgrney, Agent, or Firm-Frank R. Trifari; Carl P. 52 us. Cl. 250/333;250/213 VT; 250/338; stemhauser 250/370 51 Int. 01. H01J 31/49 L 1 S B Il 1 58 Field of Search 250/330-334, g W n? 250/338, 370, 484 213 VT;313/390, 380, tro e on the cam side 0 e target or m a1nta1n1ng 387 388the perimeter of the target at a fixed potential.

' 2 Claims, 3 Drawing Figures TRI-GLYCERINE ESJ SULFATE U.S. Patent Dec.23, 1975 3,928,768

TRI-GLYCERINE ELECTRON /GUN [0Q SULFATE JI SIGNAL IF V OUT I0 5 6 IO 3ANNuLAR ANNULAR //6 RING RING 1 )RANSPARENT H TRANSPARENT ELECTRONELECTRODE i 35;- ELECTRODE BEAM 11; RESISTIVE Iv OVERLAY Vii-'5 [I-221:;

( W SIGNAL SIGNAL I OUT OUT torgef ring-\- 'Iorge1 l ll 7 THERMALIMAGING TUBE HAVING A PYROELECTRIC TARGET AND ANNULAR POTENTIALSTABILIZING ELECTRODE The Government has rights in this inventionpursuant to Contract No. DAAK02-73-C-0335 awarded by the Department ofthe Army.

This invention relates to a thermal imaging tube, or a camera tubeemploying a pyroelectric target.

Such camera tubes have been described in [1.5. Pat. No. 3,774,043. Oneof the problems with such a tube is that the target builds up residualcharges which must be removed, for example as described in U.S. Pat. No.3,812,396.

A further problem that arises in such tubes is that even with theremoval of residual charges, the perimeter of the target may charge upin a positive direction, and actually charge up above the firstcross-over of the secondary electron emission curve. 'If this happens,the tube becomes inoperative and steps must be taken to remove thespurious charge in order to make the tube operative again.

Accordingly, it is a principal object of the invention to provide athermal imaging tube, or camera tube employing a pyroelectric target inwhich the perimeter of the target is maintained at a fixed voltage inorder to avoid positive charge build-up.

A further object of the invention is to provide a camera tube employinga pyroelectric target which is operational without a substantial delayafter potentials are applied to make it operational;

These and further objects of the invention will appear as thespecification progresses.

According to the invention, an annular evaporated metal electrode isprovided on the electron beam side of the target which is connected to asource of fixed potential relative to the cathode of the electron gun.

In one embodiment, this annular electrode is connected to the samepotential as the transparent electrode on the other side of the target.

In another embodiment, a resistive layer is evaporated over the entirebeam side of the target. With this arrangement, it is possible to pollthe target without any beam current by simply applying a voltage dropacross the target by connecting the annular ring to ground potential,and the transparent electrode to volts.

More importantly, this circuit can be used to maintain the proper polledstate if the beam is turned off for an extended period of time. Thismode of operation permits the tube to be operational immediately afterit is energized; whereas, if the target has to be polled after the tubeis energized, it may take up to five minutes to make the tube operate ina satisfactory manner.

The invention willbe described in more detail with reference to theaccompanying drawing in which:

FIG. 1 is a diagrammatic view of a tube according to the invention;

FIG. 2 is a sectional view of one embodiment of a target for the tube;and

FIG. 3 is a sectional view of another embodiment of a target for thetube.

In FIG. 1 a conventional camera tube is shown having an evacuatedenvelope 1, an electron gun 2 for providing an electron beam which isdeflected by deflection means (not shown) to scan a pyroelectric target3 of tri-glycerine sulfate (TGS) mounted on a transparent end-wall 4through which heat-radiation 5 from an object (not shown) is incident onthe target. A very thin transparent electrode 6, formed by a thin layerof conductive tin oxide evaporated on the inside surface of the window5, is provided between the target and the window.

The transparent electrode is connected to a source of potential 7through a resistor 8 across which a signal is developed in response toscansion of the target by the electron beam. This signal is coupled toan output by a capacitor 9.

In order to insure that the perimeter will always be kept at a fixedvoltage, and not charge up to, or above the first cross-over of thesecondary emission curve and thereby make the tube inoperative anannular metal electrode 10 is provided at the periphery of the target onthe beam side. This annular metal electrode is connected to thetransparent electrode 6 (see FIG. 2) so that it will always be at afixed voltage, i.e. the voltage on the transparent electrode.

FIG. 3 shows another embodiment in which a resistive layer of cadmiumtelluride (Cd Te) 11 is evaporated over the beam side of the target.With this arrangement, it is possible to poll the target without anybeam current by simply applying a voltage drop across the target byconnecting the annular ring 10 to ground potential and the transparentelectrode to l0 volts. In this mode of operation, the tube isoperational immediately after energization.

What is claimed is:

l. A thermal imaging tube comprising an evacuated envelope, an electrongun within said envelope for producing an electron beam, a thermallyresponsive target of pyroelectric material positioned at one end of saidtube to receive said electron beam on one surface thereof and a thermalimage on the opposite face thereof for producing a potential imagecorresponding to said thermal image which can be scanned by saidelectron beam, an annular conductive member encircling the periphery ofsaid target on the side facing the electron beam, means to apply apotential to said target at which said beam lands on said target, andmeans to apply a potential to said annular member which is not greaterthan the potential applied to the target and at which positiveelectrical charge build-up at the periphery of said target is preventedand said target is capable of being polled from an external source.

2. A thermal imaging tube as claimed in claim 1 in which the surface ofsaid target facing the electron beam is covered with a layer ofelectrically resistive material.

1. A thermal imaging tube comprising an evacuated envelope, an electron gun within said envelope for producing an electron beam, a thermally responsive target of pyroelectric material positioned at one end of said tube to receive said electron beam on one surface thereof and a thermal image on the opposite face thereof for producing a potential image corresponding to said thermal image which can be scanned by said electron beam, an annular conductive member encircling the periphery of said target on the side facing the electron beam, means to apply a potential to said target at which said beam lands on said target, and means to apply a potential to said annular member which is not greater than the potential applied to the target and at which positive electrical charge build-up at the periphery of said target is prevented and said target is capable of being polled from an external source.
 2. A thermal imaging tube as claimed in claim 1 in which the surface of said target facing the electron beam is covered with a layer of electrically resistive material. 